Tamper evident security bags have a wide range of uses. For example, such bags are used by businesses to carry cash, currency, checks, lo credit card receipts, etc., from the business to a bank or other depository. Such bags are also useful to provide a chain of custody for evidence from a crime scene to a laboratory and ultimately to a courtroom. In addition, security bags are often used to transport medical specimens. Security bags provide a high level of security with respect to the contents in the bag and discourage those carrying the bag, or others who have contact with the bag, from tampering or handling its contents.
Traditionally, security bags for cash and valuables management were canvas bags in which a zipper or other closure is provided with a lock and key for securing the contents of the bag. However, such canvas bags have high initial costs. The costs of bag return and handling are high, and the bags have high maintenance and replacement costs. More recently, the canvas bag has been replaced by a disposable plastic bag that has similar functionality but superior tamper evidence, compared to the earlier canvas bag.
Typically, plastic security bags are made from a sheet of high strength plastic that is folded over on itself or two or more separate sheets to form opposed front and rear bag panels. The side edges of the plastic sheet are heat sealed or otherwise welded to form a pouch or bag having an opening at one end. A header or closure flap containing adhesive is attached to the bag. After objects are placed in the bag, the flap is folded over the opening and the adhesive bonds to the outer surface of the bag to seal the objects therein. The security bag is designed so that the seal is permanent and indestructible, and the contents of the bag are removed by cutting the bag open with a knife or scissors.
Generally, attempts to break the seal between the adhesive and the outer surface of the bag stretch or otherwise distort the bag, thereby leaving evidence of tampering with the seal. However, it has been discovered that by using dry ice, freon, or other low temperature gases to lower the temperature of the adhesive closure, the adhesive freezes and loses its adhesion properties. The closure may then be opened, the contents of the bag removed, replaced or otherwise handled. As the adhesive returns to ambient temperature, it regains its adhesive properties and can then be reclosed and resealed; and therefore, the security of the bag has been violated without any evidence of the tampering.
Various solutions have been offered to provide additional evidence of tampering with the security bag. For example, as disclosed in U.S. Pat. No. 4,941,196, the bag is sealed with a special adhesive so that, when the seal is broken, portions of the adhesive remain on the surface of the bag in the form of a security pattern which remains visible after the bag is resealed. The security pattern can be achieved by utilizing special adhesives or special inks integrated within the adhesive. In another approach, as disclosed in U.S. Pat. No. 4,834,552, the adhesive is laminated with tamper evident layers of material which distort and break apart upon the seal being broken and which cannot be returned to their normal state upon resealing of the flap. While the above mechanisms are effective for providing additional evidence of tampering, the use of special adhesives, special inks, laminated adhesives and other materials add substantially to the cost of manufacturing the security bag.
Other security bag designs, for example as disclosed in U.S. Pat. No. 4,483,018, utilize an adhesive-to-adhesive seal which provides a stronger bond than simply sealing the adhesive to an outer surface of the bag. In addition, the seal area may contain perforated lines or other printed indicia that will either tear or visibly distort to leave evidence of tampering with the seal. Once again, such perforations and printed indicia add to the cost of manufacturing the security bag. Further, the adhesive-to-adhesive seal is between the flap on the bag and typically the outer surface of the front side. Therefore, the adhesive-to-adhesive seal simply covers the bag opening and does not literally seal the opening itself.